A significant need for air drying systems is found in industrial and other facilities which channel compressed air to various locations in the facility. This compressed air is normally then expelled through hoses at individual stations to clean or operate machinery and the like.
An important problem with such a system is that the air being compressed contains water. Due to the pressure increase and temperature variations in the system, the compressed air may, on some days, be very moist and even have water droplets. This is undesirable or unacceptable in many situations.
To remove this undesirable moisture, air drying devices have, in the past, been incorporated into the compressed air lines between the compressor and the end use areas. Many types of air dryers have been made available commercially and are described in the literature. The designs of these units are based on a variety of different techniques.
One such technique which has received favorable acceptance employs "double dynamic" heat exchange. In systems which employ double dynamic heat exchange, input air which is to be cooled is placed in simultaneous heat exchange relationship with a refrigerant and the already cooled output air. The primary benefits of double dynamic heat exchange units are space savings and costs savings. U.S. Pat. No. 3,818,718 is an example of an air dryer employing double dynamic heat exchange.
In the past, heat exchange units have been arranged with one passageway surrounded by another passageway. One type of such device is generally known in the field as a "shell and tube device." These units have one or more central tubes which carry refrigerant and a larger diameter cylinder or shell positioned around the central tubes. The air to be chilled and dried is ducted between the outer shell and the inner central tubes.
Such shell and tube devices and, generally, single dynamic heat exchange units are larger and more costly than desired. Added space and components are required when the entire cooling effect is provided by the refrigerant or when the input air is first cooled by heat exchange with the output air and then by heat exchange with the refrigerant.